Sulfur removal from effluent gases has become increasingly important as regulations require refineries and other petrochemical facilities to reduce their output of sulfurous compounds below previously tolerated concentrations. There are various processes known in the art to recover sulfur from numerous process gases.
For example, in a typical Claus sulfur recovery plant configuration, hydrogen sulfide is catalytically oxidized to elemental sulfur by reacting hydrogen sulfide with sulfur dioxide, which is typically generated in the same process by combustion of hydrogen sulfide with air in a reactor furnace. Because the Claus reaction represents an equilibrium chemical reaction, it is not possible for a Claus plant to convert all the incoming sulfur compounds to elemental sulfur. To increase at least to some extent the sulfur recovery, two or more stages may be coupled in series. However, depending on the configuration and initial concentration of sulfur compounds, multiple stages may not sufficiently limit output of hydrogen sulfide and/or sulfur dioxide in such plants.
Consequently, additional tail gas treatment units may be used to further reduce the output of hydrogen sulfide and/or sulfur dioxide. For example, some process configurations include heating and reducing all sulfur compounds to hydrogen sulfide, cooling and quenching, and hydrogen sulfide absorption, stripping and recycle as depicted in prior art FIG. 1. Here, sulfur components in the Claus tail gas are reduced to hydrogen sulfide in a hydrogenation reactor. The so formed hydrogen sulfide is then removed in an amine or other removal unit. While such processes are relatively simple and effectively remove sulfur from the feed gas to a significant extent, they are typically limited to sulfur dioxide concentrations of less than 1 percent in the feed gas (here: the Claus tail gas). At sulfur dioxide concentrations higher than about 1.5 percent, the temperature across the hydrogenation reactor will rise to unacceptable levels and likely damage or even completely destroy the catalyst bed. Moreover, the feed gas for such processes typically needs to be substantially free of oxygen for proper operation of the hydrogenation reactor.
Alternatively, sulfur can be removed in a process, in which sulfur and its compounds entrained in the tail gas of a Claus plant are converted to hydrogen sulfide through simultaneous hydrogenation and hydrolysis (DelaMora, et al. 1985). The so generated hydrogen sulfide is then converted to elemental sulfur in a Stretford process using an alkaline solution of salts on vanadium oxide (V2O5) and anthraquinone disulfonate to absorb and oxidize hydrogen sulfide to sulfur. The hydrogenation step is substantially the same as in the process described above; therefore, it is subjected to the same limitations. Hence, despite a relatively high rate of sulfur removal, the feed gas is generally limited to sulfur dioxide concentrations of less than 1 percent in the feed gas (here: the Claus tail gas).
Although various configurations and methods are known to reduce sulfur concentrations in effluent streams, all or almost all of them suffer from one or more disadvantages. Among other things, known processes are frequently limited to an essentially oxygen free feed gas and a sulfur dioxide concentrations of less than 1 percent in the feed gas. Therefore, there is still a need to provide improved methods and configuration to reduce the sulfur content in effluent gases.